Peptide tags that can be encoded in the genetic material of an organism for recombinant expression of proteins have been utilized for purification and identification of protein products. The advantage of a peptide tag is that the tag is covalently attached to the protein of interest without the need for additional chemical steps to label the protein. Peptide-based tags have been developed to allow for detecting a tagged protein in cell culture assays or cell lysates using antibodies that recognize the peptide tag.
While these technologies might be useful in in-situ or in-vitro assays, the applications to in-vivo analysis remain limited. Moreover, such peptide tags have limited or no functionality outside of protein purification or identification.